Electrical and electronic products (hereinafter, simply referred to as “electrical products”, but used as a concept that also includes electronic products) such as mobile phones, smartphones, cordless phones, portable media players, portable game devices, digital cameras, and digital video cameras have a sound reception part or a sound production part such as a microphone or a speaker in the housing structure thereof, an opening is provided at each corresponding position, and sound is transmitted through the opening.
As represented by the spread of smartphones, these electrical products are required to have a waterproof structure because scenes of use thereof in outdoor environments are increased. For example, in the smartphones, products generally have waterproof functions in models manufactured by domestic manufacturers and even in models manufactured by Asian manufacturers. Further, even when the products are used at home, it is expected that as electronic equipment becomes portable, the use frequency is increased in water-section environment, and accordingly, the demand for the waterproof structure as a basic design is gradually increasing.
In the related art, a filter having a mesh structure is attached to the openings in the sound production part and the sound reception part from the viewpoint of dustproofing, and the like and in order to secure sound-transmitting performance.
In order to make products waterproof, it is required to make materials for a filter attached to the opening waterproof. Further, it is also important not to hinder sound-transmitting performance, and a sound-transmitting waterproof film is known as a material having sound-transmitting performance while preventing the infiltration of water from the openings to the inside of the housing. For example, Patent Document 1 or 2 proposes a waterproof film including a polytetrafluoroethylene (PTFE) porous film. Further, Patent Document 3 discloses a sound-transmitting waterproof film in which a treatment layer with water repellency is laminated on a resin film having through-holes.